Various patents, patent applications, patent publications and other published documents are discussed below as background of the invention. No admission is made that any or all of these references are prior art and indeed, it is contemplated that they may not be available as prior art when interpreting 35 U.S.C. §102 in consideration of the claims of the present application.
1. Plastic Film Airbags
Plastic films have not previously been used to make airbags with the exception of perforated films as disclosed in U.S. Pat. No. 4,963,412 to Kokeguchi, which is discussed below.
U.S. Pat. No. 3,451,693 (Carey) describes the presence of a variable exhaust orifice in an airbag which maintains constant pressure in the airbag as the occupant is thrown into the airbag but does not disclose plastic film, merely plastic. The distinguishable properties of film are numerically described in the instant specification and basically are thinner and less weight. The material of Carey is not plastic film which is capable of arresting the propagation of a tear. In fact, it is unclear in Carey as to whether the orifice can be varied in a repeatable/reusable manner and no mention is made as to whether the stretching of the orifice area is permanent or temporary.
U.S. Pat. No. 5,811,506 (Slagel) describes a thermoplastic, elastomeric polyurethane for use in making vehicular airbags. The polyurethane is extrudable so that airbags of various shapes and sizes can be formed therefrom.
Recently issued U.S. Pat. No. 6,627,275 (Chen) describes the use of crystal gels to achieve tear resistance for airbags. This is a particular example of the teachings herein for the use of the thermoplastic elastomers to achieve tear resistance through the use of a particular subclass of such polymers. No mention is made, however, to laminate these materials with a film with a higher elastic modulus as is taught herein. Although interesting materials, they may not be practical for airbags due to their high cost. In particular, the crystal gel described in Chen is part of a class of thermoplastic elastomer (TPE) and in particular of polyester elastomers such as HYTREL™ which are discussed elsewhere herein and in the parent applications listed above. It is important to note that the particular formulations listed in Chen are probably poor choices for the blunting film portion of a laminated film used to make film airbags. This is due to their very high elasticity of 104 to 106 dynes per cm2 (see Chen at col. 21, line 4). This corresponds to the liquid crystal polymers which have an elastic modulus of above 1010 dynes per cm2. Thus, they will provide little resistance to the propagation of a tear in the higher modulus component of the laminated film and would be poor as the blunting layer.
It is important to note that liquid crystal polymers of a different sort than disclosed in Chen having quite the opposite properties would be ideal candidates for the high modulus component of a laminated film due to their inelastic nature, that is their high modulus of elasticity. Although these materials are considerably more expensive than NYLON®, for example, they are about twice as strong and therefore only half as much would be required. This would render the inner layer, for example, of a lamination with perhaps urethane as the outer layers, half the thickness and thus one eighth of the bending stiffness of NYLON®. Thus, the laminated airbag made in this manner would be considerably easier to fold and when folded, it would occupy substantially less space.
Another advantage of the more rigid liquid crystal polymers is that they can be laminated to polyurethane or other blunting materials without the need for an adhesive. This results in a significant cost saving for the laminated film and thus partially offsets the higher cost of the material compared with NYLON®, for example. Naturally, they can also be laminated to a more elastic liquid crystal polymer.
Note also that the “soft, safe, hugging, enveloping inflatable restraint cushions” described in Chen are not applicable in the form disclosed because, if used in a thin film version, it would blow up like a balloon permitting the occupant to easily displace the gas and penetrate far into the airbag. If used in a thick film version so that it does not stretch, then the advantages of the material are lost and the airbag would be similar in weight to a fabric airbag. However, if it is laminated to a more rigid material or a net as disclosed herein and in the previous patents of the current assignee, then again many of the advantages of the material are lost since the main material providing the strength to the airbag is the more rigid film or net layer. Nevertheless, providing there is not too much of a cost penalty the “elastic-crystalline gels” described in Chen might be advantageously used in the practice of the teachings of the inventions described herein for some applications. Chen is thus incorporated herein in its entirety as if it were reproduced and placed herein. Some other patents assigned to the assignee of Chen that may be relevant to the invention herein are: U.S. Pat. No. 6,552,109, U.S. Pat. No. 6,420,475, U.S. Pat. No. 6,333,374, U.S. Pat. No. 6,324,703, U.S. Pat. No. 6,148,830, U.S. Pat. No. 6,117,176, U.S. Pat. No. 6,050,871, U.S. Pat. No. 5,962,572, U.S. Pat. No. 5,884,639, U.S. Pat. No. 5,868,597, U.S. Pat. No. 5,760,117, U.S. Pat. No. 5,655,947, U.S. Pat. No. 5,633,286, U.S. Pat. No. 5,508,334, U.S. Pat. No. 5,336,708, U.S. Pat. No. 5,334,646, U.S. Pat. No. 5,324,222, U.S. Pat. No. 5,262,468 and U.S. Pat. No. 4,369,284.
Although airbags are now installed in all new vehicles and each year an increasing number of airbags are making their way into new vehicle designs, they are still basically the same design as originally invented about 40 years ago. Generally, each driver and passenger side airbag is a single chamber or at most two chambers, they are made from fabric that has sufficient mass as to cause injury to an occupant that is in the deployment path and they are positioned so that a forward-facing occupant will be protected in a substantially frontal impact. In contrast, many occupants are out-of-position and many real world crashes involved highly angular impacts, spinouts, rollovers etc. where the occupant is frequently injured by the deploying airbag and impacts other objects in the vehicle compartment in addition to the airbag.
In the out-of-position case, occupant sensors are now being considered to prevent or control the deployment of the airbag to minimize deployment induced injuries. These occupant sensors will significantly reduce the number of deaths caused by airbags but in doing so, they can deprive the occupant of the protection afforded by a softer airbag if the deployment is suppressed. Side and side curtain airbags are being installed to give additional protection to occupants in side impacts and rollovers. However, there still will be many situations where occupants will continue to be injured in crashes where airbags could have been a significant aid. What is needed is an airbag system that totally surrounds the occupant and holds him or her in the position that he or she is prior to the crash. The airbag system needs to deploy very rapidly, contact the occupant without causing injury and prevent his or her motion until the crash is over. This is a system that fills up the passenger compartment in substantially the same way that packaging material is used to prevent breakage of a crystal glass during shipment.
To accomplish this self-adjusting airbag system, the airbags must be made of very light material so that when they impact the occupant, they do not cause injury. They also must be inflated largely with the gas that is in the passenger compartment or else serious ear injuries may result and the doors and windows may be blown out. Thus, an airbag system comprised of many mini-airbags all connected together and inflated with one or more aspirated inflators that limit the pressure within each mini-airbag is needed. This is one focus of this invention. As it is accomplished, the inflators will get smaller and simpler since there will be no need for dual stage inflators. Since out-of-position occupants will not be injured by the deploying airbags, there will be no need for occupant sensors and children can safely ride in the front seat of a vehicle. The entire system will deploy regardless of the direction of the impact and the occupants will be frozen in their pre-crash positions until the crash is over.
Anticipatory crash sensors based on pattern recognition technology are disclosed in several of current assignee's patents and pending patent applications. See, for example, U.S. Pat. No. 6,343,810, U.S. Pat. No. 6,209,909, U.S. Pat. No. 6,623,033, U.S. Pat. No. 6,746,078 and US20020166710. The technology now exists to allow the identification and relative velocity determination to be made for any airbag-required accident prior to the accident occurring (anticipatory sensing). This achievement now allows airbags to be reliably deployed prior to the accident. The implications of this are significant. Prior to this achievement, the airbag system had to wait until an accident started before a determination could be made whether to deploy the airbags. The result is that the occupants, especially if unbelted, would frequently achieve a significant velocity relative to the vehicle passenger compartment before the airbags began to interact with the occupant and reduce his or her relative velocity. This would frequently subject the occupant to high accelerations, in some cases in excess of 40 Gs, and in many cases result in serious injury or death to the occupant. On the other hand, a vehicle typically undergoes less than a maximum of 20 Gs during even the most severe crashes. Most occupants can withstand 20 Gs with little or no injury. Thus, as taught herein, if the accident severity could be forecast prior to impact and the vehicle filled with plastic film airbags that freeze the occupants in their pre crash positions, then many lives will be saved and many injuries will be avoided.
The main argument against anticipatory sensors is that the mass of the impacting object remains unknown until the accident commences. However, through using a camera, or other imaging technology based on, for example, radar or terahertz generators and receivers, to monitor potentially impacting objects and pattern recognition technologies such as neural networks, the object can be identified and in the case of another vehicle, the mass of the vehicle when it is in the unloaded condition can be found from a stored table in the vehicle system. If the vehicle is a commercial truck, then whether it is loaded or not will have little effect on the severity of an accident. Also if the relative velocity of the impacting vehicles is above some threshold, then again the mass of the impacting vehicle is not important to the deployment decision. Pickup trucks and vans are thus the main concern because as loaded, they can perhaps weigh 50 percent more than when unloaded. However, such vehicles are usually within 10% of their unloaded-plus-one-passenger weight almost all of the time. Since the decision to be made is whether or not to deploy the airbag, in all severe cases and most marginal cases, the correct decision will be made to deploy the airbag regardless if there is additional weight in the vehicle. If the assumption is made that such vehicles are loaded with no more than 10% additional weight, then only in a few marginal crashes, a no deployment decision will be made when a deployment decision is correct. However, as soon as the accident commences, the traditional crash sensors will detect the accident and deploy the airbags, but for those marginal cases the occupants will have obtained little relative forward velocity anyway and probably not be hurt and certainly not killed by the deploying plastic film airbags which stop deploying as soon as the occupant is contacted. Thus, the combination of anticipatory sensor technology and plastic film airbags as disclosed herein results in the next generation self adapting safety system that maximizes occupant protection, both technologies preferably but not required to be those implemented or developed by the current assignee.
Another feature of plastic film airbags discussed below is the ability of film to be easily joined together to form structures that would be difficult or impossible to achieve with fabric such as the addition of a sheet of film to span the chambers of a side curtain airbag. It is well known that side curtain airbags are formed with chambers in order to limit the thickness of the curtain. This results in a curtain with reduced stiffness to resist the impact of the head of an occupant, for example, and to also form areas where the protection is less than other areas due to the presence of seams. Using film, these seam sections can be easily spanned without running the risk of introducing additional leakage paths in the airbag. This spanning of the chambers can produce additional chambers that can also be pressurized or the additional chambers can be left open to the atmosphere.
An analysis of a driver airbag made from two flat sheets of inelastic film shows that the maximum stresses occur in the center of the airbag where the curvature is at a minimum. Thus, the material strength and not the seal or seam strength limits the pressure that causes the airbag to fail. On the other hand, analysis of some conventional side curtain airbags has shown that the maximum stress can occur in the seams and thus the maximum pressure that the airbag can hold without bursting is limited by the material strength in the seams. This fact is at least partially the cause of excessive gas leakage at the seams of some fabric airbags necessitating the lamination of a polymer film onto the outside of the airbag. This problem is even more evident when the bag is made by continuous weaving where the chambers are formed by weaving two sheets of material together. A solution to this problem as discussed below is to first optimize the design of the seam area to reduce stresses and then to form the airbag by joining the sheets of material by heat sealing, for example, where an elastic material forms the seam that joins the sheets together. Such a joint permits the material to stretch and smooth the stresses, eliminating the stress concentrations and again placing the maximum stresses in the material at locations away from the seam. This has the overall effect of permitting the airbag to be constructed from thinner material permitting a more rapid deployment and causing less injury to an out-of-position occupant. This technique also facilitates the use of plastic film as an airbag material. Such a film can comprise a relatively inelastic, biaxially oriented layer for maximum tensile strength and a relatively elastic, polyurethane film, or equivalent, where the polyurethane film is substantially thicker than the Nylon®. This combination not only improves the blunting property discussed above but also substantially reduces the stresses in the seams (see Appendix 1).
U.S. Pat. No. 6,355,123 to Baker et al. uses reinforcement material to make the seams stronger so as to compensate for the increased stresses discussed above rather than using elastic material to smooth out the stresses as disclosed herein. Similarly, in U.S. Pat. No. 6,712,920, Masuda et al. add reinforcing strips to the inside of a seam which are attached by adhesive to the airbag beyond the sewn seam.
2. Driver side airbag
A conventional driver side airbag (also referred to herein as a driver airbag) is made from pieces of either NYLON® or polyester fabric that are joined together, e.g., by sewing. The airbag is usually coated on the inside with neoprene or silicone for the purposes of (i) capturing hot particles emitted by the inflator in order to prevent holes from being burned in the fabric, and (ii) sealing the airbag to minimize the leakage of an inflating gas through the fabric. Although such coatings are films, they differ significantly from the films disclosed herein in that they do not significantly modify the properties of the fabric airbags to which they are applied since they are thin and substantially more elastic than fabric. These airbags are conventionally made by first cutting two approximately circular sections of a material having a coating on only one side and which will form a front panel and a back panel, and sewing them together with the coated side facing out. The back panel is provided with a hole for attachment to an inflator. Fabric straps, called tethers, are then sewn to the front panel. Afterwards, the airbag is turned inside out by pulling the fabric assembly through the inflator attachment hole placing the coated side on the inside. Assembly is completed by sewing the tethers to the back panel adjacent the inflator attachment hole.
If a conventional driver airbag is inflated without the use of tethers, the airbag will usually take an approximately spherical shape. Such an inflated airbag would protrude significantly into the passenger compartment from the steering wheel and, in most cases, impact and injure the driver. To prevent this possible injury, the tethers are attached to the front and rear panels of the airbag to restrict the displacement of the front panel relative to the back panel. The result of the addition of such tethers is an airbag that has the shape of a flat ellipsoid with a ratio of the thickness of the airbag to its diameter of approximately 0.6. In the conventional airbag, the tethers are needed since the threads that make up the airbag fabric are capable of moving slightly relative to each other. The airbag is elastic for stresses that are not aligned with the warp or woof of the fabric. As a result, the fabric would distort to form an approximate sphere in the absence of such tethers.
Moreover, the above-mentioned method of manufacturing an airbag involves a great deal of sewing and thus is highly labor intensive and, as a result, a large percentage of all driver airbags are presently manufactured in low labor cost countries such as Mexico.
Many people are now being injured and some killed by interaction with the deploying airbag (See, e.g., “Warning: Too Much Safety May Be Hazardous”, New York Times, Sunday, Dec. 10, 1995, Section F, Page 8). One of the key advantages of the film airbag described herein and in the current assignee's above-referenced patents and patent applications is that, because of its much lower mass than conventional NYLON® or polyester fabric airbags, the injury caused by this interaction with the deploying airbag is substantially reduced. In accordance with the teachings of those patents and patent applications mentioned above, the driver airbag system can be designed to permit significant interaction with the driver. In other words, the film airbag can be safely designed to intrude substantially further into the passenger compartment without fear of injuring the driver. Nevertheless, in some cases, as described in U.S. Pat. No. 5,653,464, it may be desirable to combine the properties of a film airbag, which automatically attains the conventional driver airbag shape, with a fabric airbag. In such cases, interaction with the driver needs to be minimized.
Airbag systems today are designed so that ideally the airbag is fully inflated before the occupant moves into the space that is occupied by the airbag. However, most occupants are not positioned at the ideal location assumed by the airbag system designer, and also may not have the dimensions, e.g., size and weight, in the range considered for optimum airbag deployment by the airbag system designer. Many occupants sit very close to the airbags, or at least closer than expected by the airbag system designer, and as mentioned above, are injured by the airbag deployment. On the other hand, others sit far from the airbag, or at least farther away from the airbag than expected, and therefore must travel some distance, achieving a significant relative velocity, before receiving the benefit of the airbag. See for example “How People Sit in Cars: Implications For Driver and Passenger Safety in Frontal Collisions—The Case for Smart Restraints.”, Cullen, E., et al 40th Annual Proceedings, Association For the Advancement of Automotive Medicine, pp. 77–91.
With conventionally mounted airbags such as those mounted in the steering wheel or instrument panel, severe out-of-position occupant situations, for example where the occupant is resting against the airbag when deployment begins, can be handled using an occupant position sensor, such as disclosed in the current assignee's U.S. Pat. No. 5,653,462 (corresponding to published WO 94/22693) which prevents an airbag from deploying if an occupant is more likely to be seriously injured by the airbag deployment than from the accident itself. In many less severe accidents, the occupant will still interact with the deploying airbag and sustain injuries ranging from the mild to the severe. In addition, as mentioned above, some occupants sit very far from the steering wheel or instrument panel and, with conventional airbags, a significant distance remains between the occupant and the inflated airbag. Such occupants can attain a significant kinetic energy relative to the airbag before impacting it, which must be absorbed by the airbag. This effect serves to both increase the design strength requirements of the airbag and increase the injury induced in the occupant by the airbag. For these reasons, it is desirable to have an airbag system that adjusts to the location of the occupant and which is designed so that the impact of the airbag causes little or no injury to the occupant.
It is conventional in the art that airbags contain orifices or vent holes for exhausting or venting the gas generated by the inflation means. Thus, typically for frontal impact airbags within one second after the bag is inflated (and has provided its impact absorbing function), the gas has been completely exhausted from the bag through the vent holes. This imposes several limitations on the restraint system that encompasses the airbag system. Take for example the case where an occupant is wearing a seatbelt and has a marginal accident, such as hitting and severing a small tree, which is sufficient to deploy the airbag, but where it is not really needed since the driver is being restrained by his seatbelt. If the driver has lost control of the car and is traveling at 30 MPH, for example, and has a secondary impact one second or about 50 feet later, this time with a large tree, the airbag will have become deflated and thus is not available to protect the occupant in this secondary, life threatening impact.
In other situations, the occupant might be involved in an accident that exceeds the design capability of the restraint system. These systems are typically designed to protect an average-size male occupant in a 30-MPH barrier impact. At higher velocities, the maximum chest deceleration experienced by the occupant can exceed 60 G's and become life threatening. This is particularly a problem in smaller vehicles, where airbag systems typically only marginally meet the 60-G maximum requirement, or with larger or frailer occupants.
There are many cases, particularly in marginal crashes, where existing crash sensors will cause the airbag to deploy late in the crash. This can also result in an “out-of-position occupant” for deployment of the airbag that can cause injuries and possibly death to the occupant. Other cases of out-of-position occupants include standing children or the forward motion of occupants during panic braking prior to impact especially when they are not wearing seatbelts. The deploying airbag in these situations can cause injury or death to the out-of-position occupant. It is estimated that more than one hundred people have now been killed and countless more seriously injured by the deployment of the airbag due to being out-of-position.
It is recognized in the art that the airbag must be available to protect an occupant for at least the first 100–200 milliseconds of the crash and longer for rollover events. Since the airbag usually contains large vents, the inflator must continue to supply gas to the airbag to replace the gas flowing out of these vents. As a result, inflators are usually designed to produce about twice as much gas than is needed to fill the airbag for frontal impacts. This, of course, increases the cost of the airbag system as well as its size, weight, pressure in the passenger compartment and total amount of contaminants resulting from the gases that are exhausted into the automobile environment.
This problem is compounded when the airbag becomes larger, which is now possible using the film materials of this invention, so as to impact with the occupant wherever he/she is sitting, without causing significant injury, as in a preferred implementation of the design of this invention. This then requires an even larger inflator which, in many cases, cannot be accommodated in conjunction with the steering wheel, if conventional inflator technology, rather than an aspirated inflator, is utilized.
Furthermore, there is a great deal of concern today for the safety of a child in a rear facing child seat when it is used in the front passenger seat of a passenger airbag equipped vehicle. Currently used passenger side airbags have sufficient force to cause significant injury to a child sitting in such a seat and parents are warned not to use child seats in the front seat of a vehicle having a passenger side airbag. Additionally, several automobile companies are now experimenting with rear seat airbags in which case, the child seat problem would be compounded.
Airbags made of plastic film are described in the patents and patent applications referenced above. Many films are quite inelastic under typical stresses associated with an airbag deployment. If an airbag is made from a pair of joined flat circular sections of such films and inflated, instead of forming a spherical shape, it automatically forms the flat ellipsoidal shape required for driver airbags as described in U.S. Pat. No. 5,653,464. This unexpected result vastly simplifies the manufacturing process for driver airbags since tethers are not required, i.e., the film airbag is made from two pieces of film connected only at their peripheral edges. Furthermore, since the airbag can be made by heat- sealing two flat circular sections together at their peripheral edges without the need for tethers, the entire airbag can be made without sewing, thereby reducing labor and production costs. In fact, the removal of the requirement for tethers permits the airbag to be made by a blow molding or similar process. Indeed, this greatly reduces the cost of manufacturing driver airbags. Thus, the use of film for making an airbag has many advantages that are not obvious.
Films having this inelastic quality, that is films with a high modulus of elasticity and low elongation at failure, tend to propagate tears easily and thus when used alone are not suitable for airbags. This problem can be solved through the addition of reinforcement in conjunction with the inelastic films such as a net material as described in the above-referenced patents and patent applications. Other more elastic films such as those made from the thermoplastic elastomers, on the other hand, have a low modulus of elasticity and large elongation at failure, sometimes 100%, 200% or even 400%, and naturally resist the propagation of tears. Such films, on the other hand, do not form the flat ellipsoidal shape desired for steering wheel-mounted driver side airbags. As discussed in greater detail below, the combination of the two types of film through attachment using lamination, successive casting or coating, or through the use of adhesives, which can be applied in a pattern, can produce a material having both the self shaping and the resistance to tear propagation properties.
In addition to the above-referenced patents and patent applications, film material for use in making airbags is described in U.S. Pat. No. 4,963,412 to Kokeguchi. The film airbag material described in Kokeguchi is considerably different in concept from that disclosed in the current assignee's above-referenced patents and patent applications or the instant invention. The prime feature of Kokeguchi is that the edge tear resistance, or notch tear resistance, of the airbag film material can be increased through the use of holes in the plastic films, i.e., the film is perforated. Adding holes, however, reduces the tensile strength of the material by a factor of two or more due to the stress concentration effects of the hole. It also reduces the amount of available material to resist the stress. As such, it is noteworthy that the Kokeguchi steering wheel mounted airbag is only slightly thinner than the conventional driver side fabric airbag (320 micrometers vs. the conventional 400 micrometers) and is likely to be as heavy as or perhaps heavier than the conventional airbag. Also, Kokeguchi does not disclose any particular shapes of film airbags or even the airbag itself for that matter. Since his airbag has no significant weight advantage over conventional airbags, there is no teaching in Kokeguchi of perhaps the most important advantage of thin film airbags of the present invention, that is, in reducing injuries to occupants who interact with a deploying airbag. In some implementations of the film airbag of the present invention, the concept of “blunting” is used to achieve the property of arresting the propagation of a tear. See, for example, Weiss, Peter “Blunt Answer: Cracking the puzzle of elastic solids' toughness”, Science News, Week of Apr. 26, 2003 Vol. 163, No. 17. As discussed in detail below, the airbags constructed in accordance with the present teachings attain particular shapes based on the use of the inelastic properties of particular film materials and reduce tear propagation through a variety of novel methods including the use of elastic films and blunting that is achieved by combinations of films with different elastic moduli. It is also noteworthy that Kokeguchi discloses that vacuum methods can be used to form the airbag into the desired shape and thus fails to realize that the properties of inelastic film results in the airbag automatically forming the correct shape upon deployment. Also noteworthy is that Kokeguchi states that polymeric films do not have sufficient edge tear resistance and thus fails to realize that films can be so formulated to have this property, particularly those made incorporating elastomers. These limitations of Kokeguchi results in a very thick airbag that although comprised of film layers, no longer qualifies as a true film airbag as defined herein.
A “film airbag” for the purposes herein is one wherein the film thickness is generally less than about 250 micrometers, and preferably even below about 100 micrometers, for use as a driver protection airbag. As the size of the airbag increases, the thickness must also increase in order to maintain an acceptable stress within the film. A film airbag so defined may also contain one or more sections that are thicker than about 250 micrometers and which are used primarily to reinforce the thinner film portion(s) of the airbag. A film airbag as defined herein may also include a layer or layers of inelastic material and a layer or layers of elastic material (for example thermoplastic elastomers).
The neoprene or silicone coating on conventional driver airbags, as mentioned above, serves to trap hot particles that are emitted from some inflators, such as a conventional sodium azide inflator. A film airbag may be vulnerable to such particles, depending on its design, and as a result, cleaner inflators that emit fewer particles are preferred over most sodium azide inflators. It is noteworthy, however, that even if a hole is burned through the film by a hot particle, the use of an elastomer in the film material prevents this hole from propagating and causing the airbag to fail, that is by blunting the crack or tear propagation. Also, new inflators using pyrotechnic, hybrid, aspirated or stored gas technologies are now available which do not produce hot particles and produce gases which are substantially cooler than gases produced by sodium azide inflators. Also, not all sodium azide inflators produce significant quantities of hot particles.
One interesting point that also is not widely appreciated by those skilled in the art previously, is that the gas temperature from the inflator is only an issue in the choice of airbag materials during the initial stages of the inflation. The total thermal energy of the gas in an airbag is, to a first order approximation, independent of the gas temperature which can be shown by application of the ideal gas laws. When the gas initially impinges on the airbag material during the early stages of the inflation process, the temperature is important and, if it is high, care must be taken to protect the material from the gas. Also, the temperature of the gas in the airbag is important if the vent holes are located where the out-flowing gas can impinge on an occupant. The average temperature of the airbag itself, however, will not be affected significantly by the temperature of the gas in the airbag.
In certain conventional airbag deployments, the propellant which is used to inflate the airbag also is used to force open a hole in the vehicle trim, called the deployment door, permitting the airbag to deploy. Since the mass of a film airbag is substantially less than the mass of a conventional fabric airbag, much less energy is required to deploy the airbag in time. However, substantial pressure is still required to open the deployment door. Also, if the pressure now used to open the deployment door is used with film airbags, the airbag velocity once the door has been opened may be substantially higher than conventional airbags. This rapid deployment can put excessive stresses on the film airbag and increases the chance that the occupant will be injured thereby. For most implementations of the film airbag, an alternate less energetic method of opening the deployment door may be required.
One such system is described in Barnes et al. (U.S. Pat. No. 5,390,950) entitled “Method and arrangement for forming an airbag deployment opening in an auto interior trim piece”. This patent describes a method “ . . . of forming an airbag deployment opening in an interior trim piece having a vinyl skin overlying a rigid substrate so as to be invisible prior to operation of the airbag system comprising an energy generating linear cutting element arranged in a door pattern beneath the skin acting to degrade or cut the skin when activated.”
The goal of Barnes et al. is to create an invisible seam when the deployment door is located in a visible interior trim panel. This permits greater freedom for the vehicle interior designer to create the particular aesthetic effect that he or she desires. The invisible seam of Barnes et al. is thus created for aesthetic purposes with no thought toward any advantages it might have to reduce occupant injury or advantages for use with a film airbag, or to reduce injuries at all for that matter. One unexpected result of applying the teachings of this patent is that the pressure required to open the deployment door, resulting from the force of the inflating airbag, is substantially reduced. When used in conjunction with a film airbag, this result is important since the inflator can be designed to provide only sufficient energy to deploy and inflate the very light film airbag thereby significantly reducing the size of the inflator. The additional energy required to open a conventional deployment door, above that required to open a deployment door constructed in accordance with the teachings of Barnes et al., is not required to be generated by the inflator. Furthermore, since a film airbag can be more vulnerable to being injured by ragged edges on the deployment door than a conventional fabric airbag, the device of Barnes et al. can be used to pyrotechnically cut open the deployment door permitting it to be easily displaced from the path of the deploying airbag, minimizing the force of the airbag against the door and thus minimizing the risk of damage to the film airbag from the deployment door. Since Barnes et al. did not contemplate a film airbag, advantages of its use with the pyrotechnically opening deployment door could not have been foreseen. Although Barnes et al. describes one deployment door opening method which is suitable for use with an airbag made from plastic film as disclosed herein, i.e., one which requires substantially less force or pressure to open than conventional deployment doors, other methods can be used in accordance with the invention without deviating from the scope and spirit thereof.
The discussion of the self-shaping airbag thus far has been limited to film airbags. An alternate approach is to make an airbag from a combination of fabric and film. The fabric provides the tear resistance and conventional airbag appearance. The film forces the airbag to acquire the flat ellipsoidal shape desired for driver airbags without the use of tethers and permits the airbag to be assembled without sewing using heat and/or adhesive sealing techniques. Such a hybrid airbag is made from fabric and film that have been laminated together prior to the cutting operation. Naturally, the combination of a film and net, as described in the above referenced patents and patent applications, is equally applicable for the airbag described here and both will be referred to herein as hybrid airbags and belong to the class of composite airbags. The combinations of a film and fabric in this invention differ from previous neoprene or silicone coated fabric airbags in that in the prior art cases, the coating does not materially effect either the elastic modulus, stiffness, strength or tear resistance of the airbag where in the case of the invention disclosed herein, the film contributes significantly to one or more of these properties.
A finite element analysis of conventional driver side airbags (made of fabric) shows that the distribution of stresses is highly unequal. Substantial improvements in conventional airbag designs can be made by redesigning the fabric panels so that the stresses are more equalized (See, for example, Appendix 1 herein which describe inventive designs of airbags with fabric panels and relatively more equalized stresses and Appendices 1–6 of U.S. patent application Ser. No. 10/817,379 filed Apr. 2, 2004 incorporated by reference herein). Today, conventional airbags are designed based on the strength required to support the maximum stress regardless of where that stress occurs. The entire airbag must then be made of the same thickness material as that selected to withstand maximum stress condition. Naturally, this is wasteful of material and attempts have been made to redesign the airbag to optimize its design in order to more closely equalize the stress distribution and permit a reduction in fabric strength and thus thickness and weight. However, this optimization process when used with conventional fabric airbags can lead to more complicated assembly and sewing operations and more expensive woven materials and thus higher overall manufacturing costs. An example of such an airbag is that marketed by Precision Fabrics of Greensboro, NC. Thus, there is a tradeoff between manufacturing cost and airbag optimization.
As discussed in the above-referenced patents and patent applications as well as below and in Appendix 1 herein and Appendices 1–6 of the '379 application, with a film airbag manufactured using blow molding or casting techniques, for example, greater freedom is permitted to optimize the airbag vis-à-vis equalization of the stress. First, other than tooling cost, the manufacturing cost of an optimized airbag is no greater than for a non-optimized airbag and in fact frequently less since less material is required. Furthermore, the thickness of the film can be varied from one part of the airbag to another to permit the airbag to be thicker where the stresses are greater and thinner where the stresses are less. A further advantage of blow molding or casting is that the film can be made of a single constituent material. When the airbag is fabricated from sheet material, the outside layer of the material needs to be heat sealable, such as is the case with polyurethane, polyethylene or other polyolefin, or else a special adhesive layer is required where the sealing occurs.
As discussed in greater detail below in connection with the description of the invention, when the film for the airbag is manufactured by casting or coating methods, techniques familiar to those skilled in the art of plastics manufacturing are also available to produce a film where the thickness varies from one part to another in a predetermined pattern. This permits a film to be made that incorporates thicker sections in the form of a lattice, for example, which are joined together with thin film. Thus, the film can be designed so that reinforcing ribs, for example, are placed at the optimum locations determined by mathematical stress analysis.
One example of an inflatable film product which partially illustrates the self-shaping technology of this invention is the common balloon made from metalized MYLAR® plastic film found in many stores. Frequently these balloons are filled with helium. They are made by heat-sealing two flat pieces of film together as described in U.S. Pat. No. 5,188,558 (Barton), U.S. Pat. No. 5,248,275 (McGrath), U.S. Pat. No. 5,279,873 (Oike) and U.S. Pat. No. 5,295,892 (Felton). Surprisingly, the shape of these balloons, which is circular in one plane and elliptical in the other two planes, is very nearly the shape that is desired for a driver side airbag. This shape is created when the pressure within the balloon is sufficiently low such that the stresses induced into the film are much smaller than the stresses needed to significantly stretch the film. The film used is relatively rigid and has difficulty adjusting to form a spherical shape. In contrast, the same airbag made from woven material more easily assumes an approximate spherical shape requiring the use of tethers to create the shape which comes naturally with the Mylar™ balloons.
One problem with film balloons is that when a hole is formed in the balloon, it fails catastrophically. One solution to this problem is to use the combination of a film and net as described in the current assignee's above- referenced patents and patent applications. Such materials have been perfected for use as sail material for lightweight high performance sails for sailboats. One example is marketed under the trade name Bainbridge Sailcloth SL Series™, and in particular SL 500-P™, 1.5 mill. This material is a laminate of a film and a net. Such materials are frequently designed to permit heat-sealing thereby eliminating threads and the stress concentrations associated therewith. Heat-sealing also simplifies the manufacturing process for making sails. Another preferred solution is to make the airbags from a film material which naturally resists tears, that is, one which is chemically formulated to arrest a tear which begins from a hole, for example. Examples of films which exhibit this property are those from the thermoplastic elastomer (TPE) families such as polyurethane, Ecdel elastomer from Eastmen, polyester elastomers such as HYTREL™ and some metallocene-catalyzed polyolefins. For the purposes herein, a thermoplastic elastomer will include all plastic films which have a relatively low modulus of elasticity and high elongation at failure, including but not limited to those listed above. As discussed below, in many implementations, the elastomers can be laminated with NYLON® (NYLON 6,6 for example) or other more rigid film to form a composite film having the blunting property.
Applications for the self shaping airbag described herein include all airbags within the vehicle which would otherwise required tethers or complicated manufacturing from several separate panels. Most of these applications are more difficult to solve or unsolvable using conventional sewing technology. The invention described herein solves some of the above problems by using the inelastic properties of film, and others by using the elastic properties of thermoplastic elastomers plus innovative designs based on analysis including mathematical modeling plus experimentation (see Appendix 1 herein and Appendices 1–6 of the '379 application). In this manner, the problems discussed above, as well as many others, are alleviated or solved by the airbags described in the paragraphs below. Films for airbags which exhibit both the self-shaping property and also formulated to resist the propagation of a tear are made by combining a layer of high modulus material with a layer of a thermoplastic elastomer. Then, if a tear begins in the combined film, it will be prevented from propagating by the elastomer, yet the airbag will take the proper shape due to the self-shaping effect of the high modulus film. Such materials frequently exhibit blunting.
Japanese Patent No. 89-090412/12 describes fabricated cloths that are laminated in layers at different angles to each other's warp axis to be integrated with each other. Strength and isotropy are improved. The cloth is stated as being useful for automotive airbags for protecting the passenger's body. It is possible that such an airbag may have some of the self shaping properties of a driver side film airbag disclosed herein but such is not disclosed in this patent.
U.S. Pat. No. 6,607,796 and U.S. Pat. No. 6,180,044 (Hirai) describe a plastic film driver side airbag referred to as a Resin airbag and a method of making it. One layer of the film airbag is actually molded in place resulting in a variation in material thickness at the seams. This variation in thickness has also been disclosed in the current assignee's patents as listed above. The resulting bag has a variation in the shape caused by the variable width of the seam. In the current assignee's patents, a similar effect is achieved by varying the geometry of the seam as illustrated herein in FIG. 4D.
Consider now a driver side airbag that does not rotate with the steering wheel. Self-contained driver side airbag systems, such as U.S. Pat. No. 4,167,276 to Bell and U.S. Pat. No. 4,580,810 to Thuen, are designed to mount on and rotate with the steering wheel of vehicles. Such designs have the advantage of being modular so that they can be installed on many different vehicles with a modification of the steering wheel. However, because the airbag module rotates with the steering wheel, the shape of a driver side airbag must be axis-symmetrical with respect to the axis of steering wheel, as is the case with conventional driver airbags. This configuration allows the airbag to deploy and provide a uniform protection at any steering position. Usually a driver side airbag is made of two circular pieces of coated nylon cloth sewn together with tethers and becomes an approximation of an ellipsoid when inflated.
An airbag absorbs the energy of an occupant when the occupant moves forward and impacts with the airbag and the airbag deforms to wrap around the occupant. The efficiency of an airbag cushion depends not only on the stiffness and damping of the bag (which is a function of the pressure inside the bag and the exit orifices or exit valves), but also on the relative orientation and penetration of the occupant and the bag. If a large portion of the occupant torso is in contact with the bag in the early stage of a crash, a considerable amount of occupant energy can be dissipated. On the other hand, if only a small portion of the body, such as the head, is in contact with the bag, it can result in significant penetration into the bag and delay the absorption of kinetic energy. Airbags of axis-symmetrical shapes may not be optimal for occupant protection because the interaction between an airbag and an occupant is a function of the distance and the relative angle between the steering wheel and the occupant's upper torso. Another concern is that the steering wheel angle can change significantly from driver to driver.
Another problem of an ellipsoidal driver side bag is the tendency of the driver to slide off edges of the bag particularly in angle crashes. This is mainly due to the geometry of the bag and the fact that the central portion of the bag is frequently stiffer than the periphery. A solution is to have a larger airbag, like a passenger side airbag, to embrace the driver as much as possible to prevent the tendency to slide off the airbag. Such improvements can not be achieved by a driver side airbag fixed to the steering wheel because the space and the geometry are both limited.
Some vehicles, such as buses and trucks, have a very steep steering column angle. When an accident occurs and the driver moves forward, the lower part of the steering wheel close to the driver makes contact with the driver first and a great deal of abdomen or chest penetration occurs. If a conventional airbag module attached to the steering wheel is deployed, the protection of driver is limited until the upper torso of the driver bends fully forward and lands on the air cushion. This problem could be solved by modifying the angle of the steering wheel or column, but it requires a change of the structure of the steering mechanism or the installation of an additional joint in the steering column.
Inside a self-contained airbag module, the sensor is arranged so that its axis is aligned to the axis of the steering wheel. Here, the axis of the sensor is defined as the sensitive axis of the accelerometer or sensing mass. However, a ball-in-tube sensor or an accelerometer-based satellite crush zone mounted sensor used to detect frontal impacts has a sensitive axis parallel to the longitudinal axis of the vehicle. With such an arrangement, the sensor is most sensitive in the desired detecting direction. In the self-contained module mounted on the steering wheel, on the other hand, the sensitivity of the sensor to the frontal velocity change is reduced because the sensor is inclined at an angle from the crushing direction. Even though the calibration of a sensor can be selected to compensate the steering column angle, this makes the sensor more sensitive to vertical accelerations which may be undesirable.
In many cases, the driver side airbag module located on the steering wheel is large and frequently blocks the driver's view of the instrument panel behind the steering wheel. When this is the case, the addition of an airbag system to a vehicle can require modification of the steering column or the instrument panel to compensate for this reduced visibility.
The steering column of some vehicles may collapse or shift in a high-speed crash or under a tremendous crush of the front end of a vehicle. If the driver side airbag is designed to operate under normal conditions, the unexpected movement of the steering column could change the location of a deployed airbag and thus alter the relative positions of the occupant and the airbag cushion. This can result in a partial loss of airbag protection for the driver.
A recent patent application US20040026909 to Rensingoff illustrates an auxiliary airbag coming from the dashboard to support the steering wheel and provide additional protection to the driver through this supplemental airbag. Such an airbag is not disclosed to aid in supporting a much lighter steering wheel steering column as might be used in a drive-by-wire system.
3. Passenger Side Airbag
There is no known related art specifically covering passenger airbags made from plastic film.
4. Inflatable Knee Bolster
This aspect of the invention relates to a knee bolster safety apparatus for protecting the legs and lower torso of the occupant of a motor vehicle to reduce the extent and severity of injuries sustained during a crash. This invention more specifically relates to using an inflatable bolster to restrain the occupant's legs and lower torso during a survivable crash.
During a frontal impact, the occupant moves forward due to the inertia and kinematics of the crash while the front components of the vehicle structure (bumper, hood, engine cavity) begin to collapse. Knee and leg injuries occur when the body of an occupant slides or submarines forward and/or downward and the occupant's knees hit the instrument panel or structure beneath the panel. Further injuries occur when the occupant's lower torso and legs move forward such that the knees are trapped in or beneath the instrument panel just before the foot well begins to collapse. As the foot well collapses, it pushes the occupant's feet backward, causing the knees to elevate and become further trapped. As the foot well continues to crush, the loads on the trapped legs increase and cause foot, ankle, and tibia injuries. These injuries are common even with fixed knee bolsters designed to meet present knee injury criteria requirements.
Abdominal and lower torso injuries can be inflicted by the lap and lower part of the torso belts as they ride upward on the soft tissue of the occupant's torso when he or she slides forward and downward due to the forces of the frontal crash. Knee bolsters are designed to attempt to eliminate or minimize these injuries.
Airbag apparatus are generally designed under the assumption that the occupant is riding in the vehicle in a forward-facing, seated position with both feet on the vehicle floor. When an occupant is not in this position, the occupant or occupant's body part is said to be “out-of-position”. As most occupants are sometimes out-of-position, airbag apparatus which effectively restrain the occupant regardless of the occupant's position are advantageous.
During a front end collision with a standard airbag, if the occupant is restrained by a seat belt, the occupant's upper torso bends at the waist and hits the primary airbag. However, depending on the design of the vehicle seat and force of the collision, there is a tendency for an occupant to slide forward along the seat and slip below the primary airbag, sometimes even entering into leg compartment of the vehicle. Alternatively, the legs and knees of the occupant may slide or shift to one side of the seat or the other. The tendency is pronounced when the occupant is not properly restrained by a seat belt. This tendency may be referred to as “submarining”. Submarining often causes the occupant's upper torso to bend at the waist but not in a direction perpendicular to the primary airbag. When the occupant submarines, the primary airbag is less effective in protecting the occupant.
Submarining is more prevalent in vehicles which have large leg room compartments. Vehicles which have restricted leg room, such as sports cars, have a lower submarining tendency. In vehicles like sports cars, the distance between the legs and knees of the occupant and the instrument panel is shorter than the distance in vehicles like sport utility vehicles or trucks. In an accident in a sports car, the knees of the occupant often strike the instrument panel. The instrument panel then prevents submarining. Generally, the material of the sports car instrument panel deforms to some degree to help protect the legs and knees of the occupant. The area of the instrument panel which is impacted is called the knee bolster.
In order to prevent submarining in vehicles with large leg room compartments, a knee airbag system is sometimes used. A knee airbag system is generally positioned in the lower portion of the instrument panel. Knee airbag systems allow vehicle manufacturers to design vehicles with more leg room and still have safety comparable to that of vehicles with less leg room.
The knee airbag system includes an inflator, a housing, an airbag, and a trim cover panel. The housing is a conventional enclosure for securing the knee airbag components to the vehicle. The housing stores the knee airbag system components while the airbag is deflated and not in use.
The airbag provides the main structure for protecting the occupant. The bag is generally made of flexible fabric material. The material is generally a weave of NYLON® and/or polyester. Generally, multiple pieces of fabric are sewn together to form an airbag. Alternatively, the material may be woven to create a one piece airbag. Preferably, as taught herein, the airbag is formed into cells and made from plastic film.
The trim cover panel is a panel which covers the airbag and inflator within the housing and presents an aesthetic trim surface to the vehicle occupant. The trim cover panel is connected to the housing such that the pressure of the inflating airbag pushes the trim cover panel out of the way.
The inflator, once triggered, uses compressed gas, solid fuel, or their combination to produce rapidly expanding gas to inflate the airbag. As with conventional airbag systems, a knee airbag can be a large textile bag which the gas inflates like a balloon. The conventional prior art inflated knee airbag occupies some of the volume of the vehicle leg compartment. The knee airbag system may also include a fixed panel, called a load distribution panel or knee bolster panel. This panel can be made of foam and hard plastic surrounding a metal substrate. This panel can provide support to prevent submarining.
Generally, two designs are used in knee airbag systems. The first design concentrates on moving a piece of rigid material, similar to the material of the instrument panel in a sports car, close to the occupant's knees and legs thereby creating leg and knee support. This is known as a load distribution plate. The second design does not use a support plate. This design relies on the knee airbag to provide the necessary knee and leg support. Traditional designs of the knee airbag without the load distribution plate have been less successful in preventing submarining. This is due to the fact that the airbag only partially fills the volume surrounding the knees and legs of the occupant and thus the airbag can easily deform and provides less support. On the other hand, it is possible for the knees of the occupant to slip off of the load distribution plate thereby defeating its purpose. Also, if the load distribution plate is at a significant distance from the occupant's knees, the occupant can attain a significant velocity before striking the plate resulting in knee and femur injuries.
These problems are generally solved by the cellular knee bolster design described in detail herein.
It is known in the art to make an inflatable fabric single chamber knee bolster airbag without a load distribution panel. U.S. Pat. No. 3,642,303 and U.S. Pat. No. 5,240,283, for example are two of many such patents. It is also known to use an airbag to move a load distribution panel closer to the occupant. See, for example, U.S. Pat. No. 6,345,838, U.S. Pat. No. 6,471,242 and European Patent EP00684164B1.
U.S. Pat. No. 4,360,223 (Kirchoff) describes a low-mount, airbag module for the passenger side of an automobile that uses two bags that are folded within a housing that is open at one end. One of the bags is for restraining the knees of the passenger to prevent forward sliding in the event of a crash, the other bag being for restraining the torso. The knee bag is inside the torso bag and they are both attached directly to the inflator, the knee bag being arranged to be inflated first. The torso bag then is inflated to prevent forward rotation of the passenger from the hips.
Further, in accordance with Kirchoff, a pressure responsive orifice is provided in a second opening in the wall of the knee bag. This orifice controls the flow of gas through the opening in the wall of the knee bag thereby to insure a predetermined gas pressure within the knee bag, while permitting subsequent inflation of the torso bag by gases passing into the torso bag through the orifice. Thus, a knee bolster airbag is described but it is positioned inside of the main torso airbag and inflated by the same inflator.
U.S. Pat. No. 5,458,366 describes a compartmentalized airbag after the filing of current assignee's parent patent of this application, U.S. Pat. No. 5,505,485. Nevertheless, the '366 patent describes a compartmentalized airbag that functions to move a knee bolster or load distribution plate to the knees of the occupant. The occupant's knees do not contact directly the compartmentalized airbag as is the case in a preferred embodiment of the current invention as described herein below. The '366 patent correctly points out that a knee bolster airbag, referred to in the '366 patent as a reactive type knee bolster, functions on the principle of a single compartment airbag and has the disadvantage that on impact of the knees with the airbag, the airbag loses rigidity in the impact area. This is due to the gas flowing from the impact area to other parts of the airbag.
U.S. Pat. No. 6,092,836 also describes an airbag that moves a load distribution plate toward the occupant's knees. This patent points out that using known knee bolsters, the knees of an improperly seated occupant can slide off the knee bolster potentially increasing the tendency of the occupant to submarine under the instrument panel. It is important that the knee bolster capture the knees to prevent this problem, as is an object of the present invention.
Another problem pointed out by the '836 patent is the tendency, due to the point loading, for the knees in many airbag knee bolsters to penetrate too far into the bolster and therefore lose some of the energy absorbing effects. Thus, most knee bolsters use a load distribution plate for the contact point with the occupant's knees. This will also be addressed in the description of the invention below.
U.S. Pat. No. 6,170,871 describes the use of an unworkable elastic film airbag as a knee bolster. The fact that an elastic film is used results in the air flowing from the point of contact to another unloaded section which then expands as a balloon. There is also a danger that if punctured the '871 knee bolster will pop as a balloon since it will not exhibit blunting as described below. One properly designed film knee bolster, as disclosed below, makes use of a laminated film material including a layer of a high modulus of elasticity film with one or more layers of film having a low elastic modulus. The combination does not expand as a balloon as in the case of the '871 patent and thus its shape is accurately controlled. Also, if it should get punctured, the hole or tear does not propagate.
U.S. Pat. No. 6,336,653 (Yaniv et al.) describes an inflatable tubular bolster that is meant to reduce leg and knee injuries and prevent the occupant from submarining under the instrument panel. Again this design suffers from the tendency of the occupant's knees to slide off of the bolster if the accident is from an angle or if the occupant is not properly seated.
US20020149187 (Holtz et al.) describes a soft knee bolster which is basically composed of cells of fabric airbag material positioned in front of a load distribution plate. The knee bolster of the present invention also provides for a soft knee bolster but usually does not require a special load distribution or reaction plate. This patent application correctly points out that, it would advance the art to provide a soft-surface inflatable knee bolster airbag system which prevents submarining while providing a soft surface for contacting a vehicle occupant's legs and knees. It would be another advancement in the art to provide a soft-surface inflatable knee bolster airbag system which functions even though the occupant's legs and knees are “out-of-position”. A further advancement in the art would be to provide a soft-surface inflatable knee bolster airbag system which is compact, simple, and has fewer parts. The present invention provides these advancements in a novel and useful way. All of these advancements are available in the cellular bolster as first described in the current assignee's patent U.S. Pat. No. 5,505,485.
U.S. Pat. No. 6,685,217 describes a flat mattress like airbag, similar to those disclosed in assignee's prior patents, for use as a knee restraint.
Thus, there are no known knee bolster airbags that are made from plastic film or that are made from interconnecting compartments that predate those disclosed by the assignee.
5. Ceiling-Deployed Airbags
U.S. Pat. No. 5,322,326 (Ohm) describes a small, limited protection airbag manufactured in Korea. Although not disclosed in the patent, it appears to use a plastic film airbag material made from polyurethane. It is a small airbag and does not meet the United States standards for occupant protection (FMVSS-208). The film has a uniform thickness and if scaled to the size necessary for meeting U.S. Standards, it would likely become of comparable thickness and weight as the current fabric airbags.
Of particular interest, FIG. 6 shows an airbag having a shape that conforms to the human body by forming a two-fold pocket bag. Junction points are provided such that after inflation, the head of a passenger is protected by an inflated part around the upper junction point while the upper part of the passenger is covered with the other inflated part around the middle junction points and a U-shaped junction line. In contrast to some pertinent inventions disclosed below, the junction points and lines do not enable the formation of an airbag having a plurality of substantially straight or elongate compartments, or even a multiplicity of cells, which can be deploy along the side of a vehicle in order to protect the occupant(s) from injury. Rather, the junction points and lines result in the formation of a limited-use airbag which will conform only to the human body, i.e., having a section for engaging the head and a section for engaging the upper body. Other applications of junction points and lines are not contemplated by Ohm.
5.1 Side Curtain Airbag
U.S. Pat. No. 5,439,247 describes a fabric hose and quilt type airbag that is meant to protect front seat occupants in side impacts. The construction has a rectangular peripheral tube with an inner section formed by stitching the fabric together to form cells or tubes. Aside from the fact that this is made from fabric, there is no discussion as to how this airbag is supported during a crash and it appears likely that the bag will be pushed out the window by the head of the occupant. Although it is mentioned that the airbag can be deployed from either the door or the ceiling, it does not extend into the rear section of the vehicle passenger compartment. There appears to be no prior art side curtain airbags made from fabric that predate the disclosure in the current assignee's parent patents listed above. There also is no prior art for making a side curtain airbag from plastic film.
U.S. Pat. No. 6,457,745 (Heigl) is an interesting patent describing how to achieve the effects of tethers without actually having them. In this case, loose threads are used as if they were a seam to permit the weaving of a fabric airbag and at the same time to achieve control over the shape of the resulting airbag. In particular, for side curtain airbags, it is desirable to have a roughly uniform thickness across the entire front and rear seat span except where the seat back would interfere. However, to achieve this ideal would require many tethers since left to its own, the airbags would tend to form spherical-like chambers. As reported in the current assignee's patents on film airbags, this is by nature less of a problem with film since the tendency of inelastic film is to form ellipsoids rather than spheres which is the tendency of fabric. However, this is not the only advantage of film in this arena as will be seen below. Since sheets of plastic film can be easily manufactured in any thickness and since they can be easily joined using either heat or adhesive sealing, the opportunities for controlling film geometry greatly exceed that of fabric. Thus, by practicing the teachings of this invention, very substantial benefits accrue as will be shown below.
5.2 Frontal Curtain Airbags
With the exception of U.S. Pat. No. 5,322,326 discussed above, there appears to be no other prior art on ceiling- mounted airbags for frontal crash protection and none whatsoever that extend so as to offer protection for multiple occupants.
5.3 Other Compartmentalized Airbags
U.S. Pat. No. 3,511,519 (Martin) describes a large fabric airbag which is shown impacting the occupant. It does not discuss the problem of injury to the occupants due to the impact of the airbag which would certainly be the case with this design.
U.S. Pat. No. 4,262,931 (Strasser) describes two airbags joined together to cover right and center seating positions. These airbags are not mounted on the vehicle ceiling.
U.S. Pat. No. 3,638,755 (Sack) describes a two-bag airbag combination, however, one bag is contained within the other.
U.S. Pat. No. 3,752,501 (Daniel) describes an inflatable cushion device for protective interposition between a vehicle operator and the rim and hub of a vehicle steering wheel assembly. The cushion is compartmented to provide, when inflated, peripheral ring compartmentation in juxtaposition to the steering wheel rim and center compartmentation in overlying juxtaposition to the steering wheel hub. The peripheral ring compartmentation, when pressurized, provides greater resistance to collapse than the center compartmentation, whereby the peripheral ring compartmentation is adapted to guide the vehicle operator upon contact of the latter with the cushion toward the center compartmentation thereby maintaining the vehicle operator in substantially centered cushioned relationship to the steering wheel assembly under vehicle impact conditions. This airbag contains two compartments; an outer, donut-shaped ring or torus, and an inner compartment of somewhat larger volume. This is an example of a bag within a bag where an outer bag is connected to an inner bag by flapper valves.
U.S. Pat. No. 4,227,717 (Bouvier) describes a novel method of protecting a motorcycle operator with a plurality of tubular plastic or fabric airbags. These tubes deploy upward from a housing mounted on the motorcycle.
6. Rear-of-Seat Mounted Airbags
There is minimal, if any, prior art for rear-of-seat mounted airbags of the type described herein.
7. Exterior Airbags
There is minimal, if any, prior art for exterior mounted airbags made from plastic film.
8. Variable Vent
U.S. Pat. No. 3,573,885 (Brawn) describes a blowout patch assembly but not variable exhaust orifices.
U.S. Pat. No. 3,820,814 (Allgaier) describes variable exhaust vents located within the fabric airbag material.
U.S. Pat. No. 3,888,504 (Bonn) describes an inflatable occupant restraint airbag which is comprised at least in part of a woven stretch fabric which is permeable to fluid used to inflate the bag, the bag having a variable porosity which increases and decreases in relation to the fluid pressure within the bag.
U.S. Pat. No. 4,394,033 (Goetz) describes a temperature compensation system. The inflatable occupant-restraint system in a vehicle includes a generator for producing fluid under pressure placed such that a portion of the generator is outside the cushion and has a resilient venting structure for dumping increasing fractions of gas volume outside the cushion at increasing operating temperatures.
U.S. Pat. No. 4,805,930 (Takada) describes another temperature compensation system. Further, it describes stitched thread seams between fabric elements of the envelope of a vehicle safety airbag which induce localized distension and opening up of the envelope fabrics along the seams, thereby causing the film coatings of the envelope fabric to rupture along the seam and allow gas to escape and maintain a substantially constant overall maximum pressure, regardless of variations in ambient temperature.
U.S. Pat. No. 3,675,942 (Huber) describes a unidirectional valve which permits air to enter the bag, but prevents its escape in the event the pressure within the bag exceeds that of the atmosphere within the vehicle, such as by the impact of a person with the bag.
U.S. Pat. No. 4,964,652 (Karlow) describes a system for venting excessively high pressure gas incident to deployment of an airbag including a diaphragm that is rupturable upon the occurrence of a threshold pressure internally of the airbag to instantaneously release the pressure. This is a pressure relief system through the center of the module.
9. Coated Fabric Airbags
Barrier coatings which prevent, or reduce, contact of a selected substrate with a gas, vapor, chemical and/or aroma have been widely described. A recent improvement in barrier coatings is described in U.S. Pat. No. 6,087,016 and U.S. Pat. No. 6,232,389.
To date, barrier coatings have not been commercially applied in airbags made of fabric and in particular side curtain airbags made of fabric which is often permeable. It would thus be desirable to improve the impermeability of the fabric of the airbags.
In contrast to frontal impact driver and passenger airbags which only are required to retain the inflation gas or other fluid for typically a fraction of a second, the side curtain airbag must retain the inflation fluid for several seconds in order to offer protection for rollover events, for example. Also, the side curtain or ceiling-mounted airbag must deploy rapidly and pack into a small space.
It is disadvantageous that current polymer coatings used on such airbags are relatively thick thereby increasing the mass of the airbag making it difficult to pack into a ceiling space and delay the deployment of the airbag in an accident, thereby increasing the chance that an occupant will not receive the full benefit of the airbag. As a result of these disadvantages, such coatings are not optimal for use on side curtain airbags.
Much of the leakage in side curtain airbags occurs through the seams where the front and rear panels forming the side curtain airbag are joined. This is due to the methods of joining such panels which include sewing and interweaving. Thus, although the barrier coatings of this invention will reduce the leakage through the panel surfaces, and reduce the cost and mass of the airbag, alternative treatments for the seam area are also desirable as described and disclosed herein.
10. Definitions
A composite airbag is any airbag comprised of a film and a fabric, two or more films, a film and a net or other combination of two or more materials or layers such that each material contributes to the structural or tear properties of the composite. This is in contrast to the combinations of a film and fabric used previously in neoprene or silicone coated fabric airbags in that, in the prior art cases, the coating does not materially effect either the elastic modulus, stiffness, strength or tear resistance of the airbag where in the case of the composite airbag disclosed herein, the film contributes significantly to one or more of these properties. Note that the two or more layers may or may not be joined together including cases where the layers are joined during an extrusion processing step such as in co-extrusion, by a casting process, progressive coating process, or where a film layer is combined with another reinforcing material such as fibers or a woven or molded net in addition to the most common method of joining layers by adhesive.
As used herein, the term “mixture” or “coating mixture” is interpreted to include true liquid solutions, as well as colloidal dispersions, suspensions, emulsions and latexes as they are conventionally defined. For example, by “colloidal dispersion or latex”, it is meant any dispersion or suspension of particles in liquid, the particles being of a size greater than molecular scale, e.g., about 0.001 to about 0.1 micron. An emulsion generally contains particles of about 0.05 to 1.0 microns, in liquid. A “suspension” generally contains particles of greater than 1.0 micron in liquid.
A “barrier coating mixture” as used herein is meant a liquid containing dissolved or suspended solids, which is used to apply the solids to a substrate. A novel aspect of the present invention is that the barrier coating mixtures provide a better dispersion of platelet fillers in liquid at an unusually low solids content, e.g., between about 1% to about 30% solids as described in more detail below. According to this invention, once the “coating mixture” is dried, it is referred to as a “dried coating” or a “film”. The term “vapor barrier” implies a barrier to a liquid and its vapor. Conventionally, a vapor is the gas in equilibrium with a liquid at atmospheric pressure. For simplicity, as used herein, the term “vapor barrier” can be interpreted to mean a barrier to gases and chemicals as well as traditionally defined vapors, as well as a barrier to moisture, generally water or water vapor.
The term “gas barrier” includes a barrier to oxygen, nitrogen, carbon dioxide and other gases. The term “chemical barrier” includes a barrier to the migration or blooming of a molecule from one substrate to another or out of one substrate to that substrate's surface.
The term “aspect ratio” is a characteristic of every platelet material in solid form. Aspect ratio is a lateral dimension of a platelet filler particle, e.g., mica flake, divided by the thickness of the platelet. The term “high aspect ratio” refers to a platelet filler whose lateral dimension divided by thickness is greater than 25. The aspect ratio of any filler is an inherent property of the selected filler. For example, MICROLITE® 963++ aqueous vermiculite solution [W. R. Grace] has a characteristic aspect ratio of about 10,000 or dimensions of 10–30 μm×10 Å.
Intercalation is defined as the state of a coating composition in which polymer is present between each layer of a platelet filler. Intercalation can be defined by the detection of an X-ray line, indicating a larger spacing between vermiculite layers than in the original mineral. The term “exfoliation” is defined for layered fillers as the complete separation of individual layers of the original particle, so that polymer completely surrounds each particle. Preferably, so much polymer is present between each platelet, that the platelets are randomly spaced. No X-ray line appears because of the random spacing of exfoliated platelets. In some circumstances, the filler can exfoliate when dispersed in an aqueous or non-aqueous medium. This would result in a higher aspect ratio than that of a solid particle before dispersion.
The term “effective aspect ratio” relates to the behavior of the platelet filler when incorporated into a binder. The platelet may not exist in a single platelet formation, but in many forms, such as a bundle of 10–50 platelets or hundreds of platelets, referred to as agglomerates. If the platelets are not in the single layer form, the aspect ratio of the entire bundle or agglomerate is much lower than that of the single layer particle. Therefore, the aspect ratio of the particles in a binder is referred to as an effective aspect ratio. The effective aspect ratio is determined by plotting the experimental data versus theoretical model, such as described by E. L. Cussler et al, J. Membrane Sci., 38:161–174 (1988). A graph of reduction in permeability versus the volume % of filler in the binder generates theoretical curves for each effective aspect ratio. The graph predicts an effective aspect ratio for the experimental data (see FIG. 26).
It is important in the understanding of the effects of the coatings of this invention to differentiate between “effective aspect ratio” and “aspect ratio”. The aspect ratio is characteristic of a platelet material in the solid form or one platelet and can be determined by light scattering techniques or microscopy. The term “effective aspect ratio” is much different in that it relates to the behavior of the platelet when incorporated into a binder. It may no longer be a single platelet but instead bundles of platelets referred to as agglomerates. This value is determined using experimental permeability data plotted versus theoretical behavior of the platelet. For example, experimental data when plotted versus the theoretical model of the platelet in the binder [see E. L. Cussler et al, J. Membrane S., 38:161–174 (1988)] is directly related to the barrier improvement of the coating through Cussler's theoretical model.
Most commercially available fillers have aspect ratios ranging from 25 up to 10,000. However, the effective aspect ratio of these fillers is much lower when incorporated into a binder and is directly related to the barrier improvement due to the platelet filler, generally resulting in reduced barrier properties. It is important to distinguish between these terms for barrier coatings containing platelet fillers.
Much of the disclosure above and below involving particular barrier coatings is based on U.S. Pat. No. 6,087,016 and U.S. Pat. No. 6,232,389. However, the invention is not limited to airbags including the barrier coatings described in these patents and encompasses airbags including any comparable barrier coatings and any barrier coatings encompassed by the claims.